HomeNew HampshireMerrimack County

Merrimack County, New Hampshire

A shallow water table limits basements on 49% of Merrimack County's mapped land, a higher share than 66% of US counties and the 2nd highest of 10 New Hampshire counties. Shrink-swell clay limits houses without basements on 2%.

0.3% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list 11 flood losses here since 2016. 54% of homes were built before 1980, against 50% nationally; the median home dates from 1977.

Data as of October 13, 2026 · sources

2%

expansive clay: shrink-swell limits slab homes

49%

high water table: limits basements

0%

in drought, October 13, 2026

54%

of homes built before 1980

Soil under Merrimack County

Expansive clay (limits slab homes)2.0%
High water table (limits basements)49.4%
Septic fields very limited93.0%
Clay swell (LEP, by area)1.3%
High-swell land (LEP 6%+)4.8%
Mapped soil611,117 acres
Soil seriesShare hereSeries nationally: high water table
Tunbridge7%n/a
Lyman6%n/a
Becket6%n/a
Skerry4%n/a
Montauk3%n/a
Millsite3%n/a
Belknap County: 42%Hillsborough County: 28%Sullivan County: 26%Strafford County: 39%Rockingham County: 48%Cheshire County: 27%Grafton County: 29%Carroll County: 36%Merrimack County BelknapHillsboroughSullivanStraffordRockinghamCheshireGraftonCarrollMerrimack
Merrimack County (heavy outline) and nearby counties, shaded by high water table share.under 10%10-25%25-40%40-60%60%+

How we count · survey areas NH609 (2025-09-10)

What the numbers mean here

On 49% of Merrimack County's mapped land, soil stays saturated within about 6 feet of the surface for part of the year, which is basement depth.

Rain over the 12 months to August 2026: 38.63 in, 8.55 in below the 1991-2020 average year of 47.18 in.

USDA rates 93% of the land very limited for septic absorption fields.

Drought

0.3% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 52 of the last 52 weeks; the most was 100% of its area, in 11 weeks, most recently on the June 9, 2026 map.

October 21, 2025Share of area in drought, weeklyOctober 13, 2026
Category, October 13, 2026Share of county
D0 abnormally dry or worse100%
D1 moderate drought or worse0.3%
D2 severe or worse0%
D3 extreme or worse0%
D4 exceptional0%

Flood losses since 2016

11 flood losses since 2016, $107,042 paid. The worst year was 2021, with 3.

YearFlood losses
20161
20172
20183
20190
20200
20213
20221
20231
20240
20250
2026 to date0

Rain

Average year, 1991-202047.18 in
12 months to August 202638.63 in (-8.55)
202540.27 in (-6.91)
Wettest year since 18952006: 63.14 in
Driest year since 18951965: 28.85 in
Days with 1 inch or more, normal at CONCORD MUNI AP (12 mi away)9.5

Homes

Housing units66,497
Median year built1977
Built before 198054%
Built 2000 or later20%
Owner-occupied74%
Median value, owner-occupied$367,600
Single-family detached63%

What repairs cost

Published ranges from cost guides, not quotes. More sources, and where they disagree.

WorkRangeSource
Basement waterproofing, US $3,000 to $10,000 Fixr, February 6, 2026
Sump pump installation, US $800 to $2,000 Fixr, January 31, 2025
Crawl space encapsulation, US $2,000 to $8,000 Fixr, August 29, 2025

Nearby counties

PlaceDistanceExpansive clayHigh water table
Belknap County, NH 20 mi 2% 42%
Hillsborough County, NH 27 mi 3% 28%
Sullivan County, NH 28 mi 2% 26%
Strafford County, NH 32 mi 1% 39%
Rockingham County, NH 36 mi under 1% 48%
Cheshire County, NH 39 mi 4% 27%
Grafton County, NH 44 mi 1% 29%
Carroll County, NH 46 mi 2% 36%

Sources: USDA SSURGO (September 10, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status